Characterization of an Sinorhizobium meliloti acid sensitive mutant

CASTELLANO, L.; DRAGHI, W.O.; LOZANO, M.J.; GIUSTI, M.A.; TORRES TEJERIZO, G.A.; PISTORIO, M.; LAGARES, A.; DEL PAPA, M.F.

Mar del Plata, Argentina

Congreso; XLIII Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2007

Sociedad Argentina de Bioquímica y Biología Molecular

Soil acidity may reduce the productivity of alfalfa plants mainly derived from the marked acid-sensitivity of the prokaryote symbiont which cannot grow at pH below 5.5. The identification of genetic determinants of tolerance in Sinorhizobium meliloti has been considered as an important target of research. The molecular mechanisms of acid tolerance in S.meliloti has shown to be complex and need additional fundamental research to understand how rhizobia protect themselves from the extracellular hydrogen ions, and how they infect the plant symbiont. To advance on the genetics of acid tolerance in S. meliloti we generated a collection of Tn5B20mutants and we screen the collection for acid sensitive phenotypes. Three mutants out of 2,000 clones failed to grow on minimal medium at pH 5.5 but not at neutral pH. Genetic analysis of one of them, namely mutant LPU630, showed a transposon insertion within an ORF with sequence similarity to a putative ABC transporter with an unusual central domain located immediatelyupstream of a putative transcriptional regulatory protein. We will now investigate the impact of the new marker on the ability of rhizobia to tolerate other abiotic stresses, and on the capacity to do symbiosis under moderate acid media.